This is not bug. The timeout is default 5 second defined in:
SocketStream::$timeout = 5;

There is no configuration here to set this time nor any setter. Increase value anyway.

@seddighi78 can you confirm temporary solution ?

@michaljusiega I'm using a try-catch to control the throws of the mailer. the mail was successfully sent but time out happened.

Yes because your SMTP server probably analyze your mail too slowly so you got a exception for this reason.

Do I have to wait for this problem or is there a right solution?

@seddighi78 this is not a bug, as @michaljusiega has mentioned, your server is taking too long to responed and symfony mailer is timing out.

if you want to increase the timeout, you can do so using :

$transport->getStream()->setTimeout($timeoutInSeconds);

@azjezz How can i change timeout from event listener or controller? I can't change timeout from configuration

I would highly recommend to fix the latency of the server if possible. If not, configure default_socket_timeout in the php.ini file (which will be available for SMTP server as of Symfony 5.1). In the meantime, using the snippet given by @azjezz will work as well.

Thank you @fabpot

The only way of solving this in 4.4 is creating a custom factory that configures the timeout of the socket ?

Here's my problem with this: Application is running on Symfony 5.0 and files between 3-4 MB need to get attached. In the development environment, we are using Mailhog on a Docker container - the former being notoriously slow at processing emails with attachments. In this scenario, we are getting a ["/app/vendor/symfony/mailer/Transport/Smtp/Stream/AbstractStream.php","Connection to "localhost:1025" timed out."] error from our Console command. Emails are still being sent and received successfully.
default_socket_timeout is set to 60 in the ini settings used by PHP CLI, but this seems to be ignored.

I solved it for v4.4 by setting timeout in the decorated EsmtpTransportFactory::create method.
I blogged about it.